.
where dij is the Euclidian distance between patches j and i and α is the parameter of the negative exponential dispersal kernel, which was set to 1 km−1 (see Jousimo et al. (2014) for more details).Aj , is the square root transformation of area (m2) of habitat patch j .
The Åland archipelago is highly fragmented and consists of the main island and smaller islands that jointly form 16 regional districts of similar size. To capture possible spatial variation among the regions within the islands, we used regional district as a spatial unit. In our sampling area, there were 10 regional districts (Eckerö (12), Finström (41), Hammarland (38), Jomala (10) Lemland (37), Lumparland (49), Maarianhamina (11), Saltvik (19), and Sund (46), with the number of visited populations within each regional district given in parenthesis).